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"SLEUTHING OUT Contamination" mentioned the difference in perchlorate samples (C&EN, Sept. 1, page 49). Readers may be interested in a brief history of synthetic perchlorate.
Before World War II, the U.S. imported all its perchlorate from Sweden; it was used to make perchloric acid and other perchlorate salts. At the start of the war, this imported material was no longer available. At least two different companies started making sodium perchlorate from sodium chlorate, which was derived from sodium chloride. One was in the Niagara Falls, N.Y., area and the other in Columbus, Ohio. The former facility was much larger than the latter.
In the 1960s, the need arose for more ammonium perchlorate than could be produced. Consequently, operations were set up in the Henderson, Nev., area to produce the material for rocket propellants for intercontinental ballistic missiles and eventually for the space program. After a disastrous fire and explosion, the operation was removed to a less populated area.
Obviously, the chlorine found in perchlorate will depend on the source used for the sodium chloride, and the oxygen in the perchlorate will be determined by the water supply that was used. No atmospheric oxygen could have been used. There are many possible combinations of sources, but some may be from many years ago.
Loren C. McBride
Surfside Beach, S.C.